17693-79-7Relevant articles and documents
Mechanism of dihydrogen cleavage by high-valent metal oxo compounds: Experimental and computational studies
Collman,Slaughter,Eberspacher,Strassner,Brauman
, p. 6272 - 6280 (2001)
The oxidation of dihydrogen by metal tetraoxo compounds was investigated. Kinetic measurements of the oxidations of H2 by MnO4- and RuO4, performed by UV-vis spectroscopy, showed these reactions to be quite rapid at 25 °C (k1 ≈ (3-6) x 10-2 M-1 s-1). Rates measured for H2 oxidation by MnO4- in aqueous solution (using KMnO4) and in chlorobenzene (using nBu4NMnO4) revealed only a minor solvent effect on the reaction rate. Substantial kinetic isotope effects [(kH2/kD2 = 3.8(2) (MnO4- aq), 4.5(5) (MnO4-, C6H5C1 soln) and 1.8(6) (RuO4, CCl4 soln)] indicated that H-H bond cleavage is rate determining and that the mechanism of dihydrogen cleavage is likely similar in aqueous and organic solutions. Third-row transition-metal oxo compounds, such as OsO4, ReO4-, and MeReO3, were found to be completely unreactive toward H2. Experiments were performed to probe for a catalytic hydrogen/deuterium exchange between D2 and H20 as possible evidence of dihydrogen σ-complex intermediates, but no H/D exchange was observed in the presence of various metal oxo compounds at various pH values. In addition, no inhibition of RuO4-catalyzed hydrocarbon oxidation by H2 was observed. On the basis of the available evidence, a concerted mechanism for the cleavage of H2 by metal tetraoxo compounds is proposed. Theoretical models were developed for pertinent MnO4- + H2 transition states using density functional theory in order to differentiate between concerted [2 + 2] and [3 + 2] scissions of H2. The density functional theory calculations strongly favor the [3 + 2] mechanism and show that the H2 cleavage shares some mechanistic features with related hydrocarbon oxidation reactions. The calculated activation energy for the [3 + 2] pathway (ΔH? = 15.4 kcal mol-1) is within 2 kcal mol-1 of the experimental value.
Thermal decomposition of H3O- produced in reaction of OH- with H2CO
Viggiano, A. A.,Miller, Thomas M.,Miller, Amy E. Stevens,Morris, Robert A.,Paulson, John F.,et al.
, p. 357 - 361 (2007/10/02)
The ion-molecule reaction OH- + H2CO H3O- + CO has been studied at 300 K with isotropic labeling of reactants.The H3O- product is only observed in small abundance because the ion dissociates into HO- + H2 upon multiple collisions in a helium buffer gas.Without isotopic labeling, the pseudo-first-order kinetics plots for the reactions of OH- with H2CO and OD- + D2CO were found to be curved as a result of the regeneration of OH- or OD- reactant.A scavenger technique was used to remove the H3O- (or D3O-) produced prior to dissociation, to reveal the true first-order attenuation of OH- (or OD-) in reaction with H2CO (or D2CO).The rate constant for the OH- + H2CO reaction is 7.6x10-10 cm3 s-1, and for OD- + D2CO is 5.7x10-10 cm3 s-1.For the isotopically mixed cases OH- + D2CO and OD- + H2CO, the rate constants are equal to 1.3x10-9 cm3 s-1, about twice as large as those for the reactions involving only a single hydrogen isotope, indicating that isotopic exchange is an important process.The rate constants for the thermal dissociation of H3O- and D3O- in helium were found to be 1.6x10-12 and 1.1x10-12 cm3 s-1, respectively, within a factor of 2.The results are discussed in terms of other thermal dissociation reactions of ions.
